Detector senses tiny sample of explosives

Portland, Ore. - While the increased threat from terrorism today has airports X-raying all luggage for weapons, there has been no fast, practical way for security personnel to scan baggage for the presence of bombs.

Now, a Purdue University research team claims to have developed a sensor that is fast enough to detect tiny amounts of residue from explosives, using standard mass spectrometers outfitted with a special puff-and-sniff, two-nostril "nose."

"We have reduced to about five seconds the amount of time it requires to sniff the surface of a piece of luggage and determine whether a hazardous substance is likely to be inside," said Purdue chemistry professor R. Graham Cooks, who designed the device. "Devices using our patented technique could screen suspect packages in airports, train stations and other likely places. It also works on skin and clothing, so it could also help determine whether an individual has been handling hazardous chemicals."

Cooks developed the method with the assistance of the doctoral candidates in his research group (www.chem.purdue.edu/cooks), Ismael Cotte-Rodriguez, Zoltan Takats, Nari Talaty and Huanwen Chen.

In the lab, mass spectrometers can easily detect trace residues of explosives brushed from the hand of someone loading a suitcase, thus determining whether a hazardous substance is likely to be inside. But either the suitcase must be swabbed or other time-consuming methods must be used to prepare a sample taken from its surface.

In contrast, the Purdue researchers puff a gas mixture of ions onto the suitcase as it passes by, thereby using the ionic charge to eject molecules from the surface of the suitcase and into the two-nostril nose of the mass spectrometer.

"Using our spray technique with a tandem mass spectrometer gives this method the sensitivity and turnaround time needed to quickly confirm the identity of particular explosives," said Cooks.

The technique, called desorption electrospray ionization (Desi), detects picogram (trillionths of a gram) traces of the explosives TNT, RDX, HMX and PETN, which are found within the plastic compositions of C-4, Semtex-H and Detasheet. An ionized solvent that specifically pinpoints the suspected explosives is sprayed on the suitcase. Two mass spectrometers used in tandem-the nostrils of the device's nose-reduce false alarms to negligible levels, according to Cooks, who claims the technique worked directly on a wide variety of surfaces without swabbing or pretreating them, including metal, plastic, paper and polymers.

Cook, along with Purdue researchers Takats, Justin Wiseman and Bogdan Gologan, developed a long tubelike wand as the nose. The wand both sprays the ionized gas and sucks up the ionized compounds that come off the surface of the material being tested. The group also redesigned the mass spectrometer so that it only weighed 40 pounds, allowing it to be carried to the point of inspection.